Steam reformer bypass plenum and flow controller

ABSTRACT

A reforming unit for a fuel cell system is provided. The reforming unit may comprise a reforming section, a heat exchanging section and a bypass plenum. The reforming section reforms a hydrocarbon containing fuel. The heat exchanging section effects a heat transfer between a fluid flowing therethrough and the fluid flowing through the reforming section, the bypass plenum, or both. The bypass plenum provides a flowpath for the hydrocarbon-containing fuel to bypass the reforming section. The bypass plenum may comprise a flow restrictor in the outlet of the bypass plenum to control the amount of fluid communication between the outlet of the bypass plenum and the outlet of the reforming section.

FIELD

This disclosure generally relates to fuel cells. More specifically, thisdisclosure is related to systems and methods which may supportinternally-reforming fuel cells.

BACKGROUND

A fuel cell is an electrochemical system in which a fuel (such ashydrogen) is reacted with an oxidant (such as oxygen) at hightemperature to generate electricity. One type of fuel cell is the solidoxide fuel cell (SOFC). The basic components of a SOFC may include ananode, a cathode, a solid electrolyte, and an interconnect. The fuel maybe supplied to the anode, and the oxidant may be supplied to the cathodeof the fuel cell. At the cathode, electrons ionize the oxidant. Theelectrolyte comprises a material that allows the ionized oxidant to passthrough to the anode while simultaneously being impervious to the fluidfuel and oxidant. At the anode, the fuel is combined with the ionizedoxidant and releases electrons to be conducted back through an externalcircuit to the cathode. Additional heat, generated in the stack fromohmic losses, is transferred to the cathode stream. This heat can eitherbe used to facilitate other chemical reactions within the system, it canbe exhausted from the system, or is radiated to the environment.

A SOFC may be structured, e.g., as a segment-in-series or in-planeseries arrangement of individual cells. The oxidant is typicallyintroduced at one end of the series of cells and flows over theremaining cells until reaching the cathode exhaust outlet. Each fuelcell transfers a portion of the ohmic heat into the oxidant therebyraising its temperature, and forming a temperature gradient whichincreases from the oxidant inlet to the exhaust. Consequently, atemperature gradient may also develop in the fuel cell which increasesfrom the oxidant inlet to the oxidant exhaust. This temperature gradientmay cause thermal stresses leading to degradation or failure of the fuelcell components.

The anode of a SOFC may be a mixed cermet comprising nickel and zirconia(such as, e.g., yttria stabilized zirconia (YSZ)) or nickel and ceria(such as, e.g., gadolinia doped ceria (GDC)). Nickel, and othermaterials, function not only to support the chemical reaction betweenthe fuel and the ionized oxidant but also have catalytic propertieswhich allow the anode to reform a hydrocarbon fuel within the fuel cell.One method of reforming the hydrocarbon fuel is steam reforming ofmethane (CH₄) to form syngas, an endothermic reaction:CH₄+H₂0→CO+3H₂ ΔH°=206.2 kJ/mole

The heat necessary for the reformation of methane could be supplieddirectly from the ohmic heat generated within the fuel cell stack. Thisdirect heat transfer would help cool the stack, reduce thermal stresses,and enable more of the fuel cell stack to operate at the optimaloperating temperature for the fuel cells. However, in-stack reformingintroduces several technical challenges. Unreformed methane must besupplied in the correct amount to avoid excessively cooling of the fuelcell and in the correct manner to avoid localized cooling. Additionally,under the right conditions, hydrocarbon fuels have a propensity to formcarbon, for example via thermal cracking:C_(x)H_(2x+2)→C+(x+1)H₂

Carbon formation can cause fouling and degradation of fuel cellcomponents through anode delamination, metal dusting and other failuremechanisms.

Consequently, supplying a mixture of a syngas reformed external to thefuel cell and an unreformed fuel to the anode may provide better abalance of system performance and durability than supplying eitherreformate or unreformed fuel alone. However, the ratio of reformed andunreformed fuel must be precisely controlled. If the ratio is too high,the large temperature gradient across the fuel stack will remain. If itis too low, carbon formation will compromise fuel cell performance andlife.

Additionally, assemblies for controlling the flow rate a fluid typicallyinclude needle or other types of valves and orifice plates. Someadjustable orifice plates comprise rotating plates wherein each platedefines an opening. The alignment of plate openings determines theeffective flow area of the orifice. However, these solutions are notsuitable for the high temperature and pressure conditions of anoperating fuel cell and are prone to leakage.

There remains a need for precise control of the ratio of reformed andunreformed fuels delivered to a fuel cell stack to ensure that theproper amount of reforming occurs internally to the fuel cell.Additionally, there remains a need for systems and methods to achievethis precise control.

In accordance with some embodiments of the present disclosure, areformer with a bypass is provided. The bypass may contain a flowcontroller that restricts the bypass flow. The flow controller may beadjustable to control the flow rate of the fluid through the bypass,thereby enabling precise control of the ratio of reformate andunreformed fuels supplied to the fuel cell stack. This design permitssome of the disclosed embodiments to accommodate a wide range ofin-stack reforming fuel cell designs and minimizes the risk for carbonformation.

In accordance with some embodiments of the present disclosure, effectiveand adjustable means are provided that control the fluid flow ratewithin a reformer bypass in a high temperature and pressure environment.

In accordance with some embodiments of the present disclosure, areformer unit is provided. The reformer unit may have a reformingsection, a heat exchanging section, and a bypass section. The reformingsection may reform a hydrocarbon-containing fuel, and have an inlet influid communication with a source of hydrocarbon fuel and an outlet influid communication with an anode inlet of a fuel cell stack. The heatexchanging section may heat a fluid flowing in the reforming section, inthe bypass section, or both, and may have an inlet in fluidcommunication with an exhaust of a cathode of a fuel cell stack, and anoutlet adapted for fluid communication with an inlet of a cathode of afuel cell stack. The heat exchanging section is in thermal communicationwith said reforming section (or said bypass section or both) to effectheat transfer between the fluids flowing in each section. The bypasssection provides a flow path for the hydrocarbon-containing fuel aroundthe reforming section, and has an inlet in fluid communication with thereforming section inlet, an outlet in fluid communication with thereforming section outlet, and a variable orifice flow controllerpositioned in the bypassing flow path.

In accordance with some embodiments of the present disclosure, avariable orifice flow controller for controlling the flow of a hightemperature, high pressure, or both fluid is provided. The flowcontroller may comprise an upstream connector, a downstream connectorand an interconnector. The upstream connector may have cylindricaltubular portion defining a conduit in fluid communication with a flowpath of high temperature fluid and a frusto-conical portion defining aplurality of conduits in fluid communication with the conduit. Thedownstream connector may define a frusto-conical cavity for receivingthe frusto-conical portion of said upstream connector and a plurality ofconduits in fluid communication with said cavity. The interconnector mayprovide a fluid-tight connection when the frusto-conical portion of theupstream connector is received within the cavity defined by saiddownstream connector. The amount of fluid communication between theplurality of conduits defined by the downstream and upstream connectorsis selected by the radial alignment between the upstream and downstreamconnectors when in a gastight connection.

In accordance with some embodiments of the present disclosure a variableorifice flow controller for controlling the flow of a high temperature,high pressure, or both gas is provided. The flow controller may comprisean upstream connector, a downstream connector, a disc, and aninterconnector. The upstream connector may have cylindrical tubularportion defining a conduit in fluid communication with a flow path ofhigh temperature fluid and a frusto-conical portion defining a pluralityof conduits in fluid communication with the conduit. The downstreamconnector may define a frusto-conical cavity for receiving thefrusto-conical portion of said upstream connector and a conduit in fluidcommunication with the cavity. The disc may define a plurality ofconduits and may be adjacent to a face of the frusto-conical portion ofsaid upstream connector in a selected radial alignment such that theplurality of conduits defined by the disc are in fluid communicationwith the plurality of conduits defined by the frusto-conical portion ofthe upstream connector and the conduit define by the downstreamconnector. The interconnector may provide a fluid-tight connection whenthe frusto-conical portion of the upstream connector is received withinthe cavity defined by said downstream connector. The amount of fluidcommunication between the plurality of conduits define by the disc andthe plurality of conduits defined by the frusto-conical portion of saidupstream connector is selected by the radial alignment of the conduitswhen in a gastight connection.

In accordance with some embodiments of the present disclosure, areformer unit for a fuel cell is presented. The reformer unit maycomprise a reforming section, a heat exchanging section, and a bypassplenum. The reforming section reforms a hydrocarbon-containing fuel andhas an inlet in fluid communication with a source ofhydrocarbon-containing fuel and an outlet plenum in fluid communicationwith an anode inlet of a fuel cell stack. The heat exchanging sectionheats a fluid flowing in the reforming section, the bypass plenum, orboth. The heat exchanging section has an inlet in fluid communicationwith the exhaust of a cathode and an outlet adapted for fluidcommunication with an inlet of cathode of the fuel cell stack. The heatexchanging section is in thermal communication with the reformingsection and the bypass plenum to effect a heat transfer. The bypassplenum provides a flow path for the hydrocarbon-containing fuel tobypass the reforming section and has an inlet in fluid communicationwith the reforming section inlet, an outlet in fluid communication withthe reforming section outlet plenum and a flow restrictor in theflowpath between the outlet of the bypass plenum and the outlet plenumof the reforming section.

In accordance with some embodiments of the present disclosure, a flowrestrictor for restricting the flow of a high temperature fluid throughan orifice providing fluid communication between two plenums isprovided. The flow restrictor may comprise a connector mounted to a wallof a first plenum, a fitting, an elongated flow restricting member, andan internally threaded sealing nut. The connector comprises a firstportion defining a cylindrical cavity having a threaded portion and asecond portion which defines a frusto-cylindrical cavity incommunication with the cylindrical cavity. The fitting comprises afrusto-conical end portion that is positioned within the frusto-conicalcavity and defines an axial slot. The elongated flow restricting membercomprises a cylindrical threaded portion positioned and threadablyengaged with the cylindrical cavity, a portion extending from one end ofsaid cylindrical portion into the axial slot and a tapered portionextending from the other end of the cylindrical portion through theorifice. The axial alignment of the tapered potion and the orifice isselectable by rotating the flow restricting member relative to theconnector. The internally threaded sealing nut engages an externalthreaded portion of the connector and provides a fluid-tight sealbetween the fitting and the connector.

In accordance with some embodiments of the present disclosure, areforming unit for a fuel cell system is provided. The reforming unitmay comprise a reforming section, a heat exchanging section and a bypassplenum. The reforming section reforms a hydrocarbon containing fuel. Theheat exchanging section effects a heat transfer between a fluid flowingtherethrough and the fluid flowing through the reforming section, thebypass plenum, or both. The bypass plenum provides a flowpath for thehydrocarbon-containing fuel to bypass the reforming section. The bypassplenum may comprise a flow restrictor in the outlet of the bypass plenumto control the amount of fluid communication between the outlet of thebypass plenum and the outlet of the reforming section.

These and many other advantages of the present subject matter will bereadily apparent to one skilled in the art to which the disclosurepertains from a perusal of the claims, the appended drawings, and thefollowing detail description of the embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a system diagram of a fuel cell system with a reformer havinga bypass in accordance with some embodiments of the present disclosure.

FIGS. 2A and 2B are perspective views of a reformer having a bypass inaccordance with some embodiments of the present disclosure.

FIG. 3 provides two perspective views of a flow controller in accordancewith some embodiments of the present disclosure.

FIG. 4 provides two cross-section views of the flow controller of FIG. 3in accordance with some embodiments of the present disclosure.

FIG. 5 illustrates a perspective view of the assembled flow controllerof FIG. 3 in accordance with some embodiments of the present disclosure.

FIG. 6 illustrates a disassembled, perspective view of a flow controllerin accordance with some embodiments of the present disclosure.

FIG. 7 illustrates an assembled, perspective view of the flow controllerof FIG. 6 in accordance with some embodiments of the present disclosure.

FIG. 8 illustrates two perspective views of a reformer unit having abypass plenum in accordance with some embodiments of the presentdisclosure.

FIG. 9 illustrates the inlet plenum of a reformer unit having a bypassplenum in accordance with some embodiments of the present disclosure.

FIG. 10 illustrates a close-up view of a bypass plenum in accordancewith some embodiments of the present disclosure.

FIG. 11 illustrates exploded perspective and assembled cross-sectionalviews of a flow restrictor in accordance with some embodiments of thepresent disclosure.

FIG. 12 provides a close-up view and a cross-sectional view of theoutlet of a bypass plenum in accordance with some embodiments of thepresent disclosure.

Referring to the drawings, some aspects of non-limiting examples of afuel cell system in accordance with an embodiment of the presentdisclosure are schematically depicted. In the drawings, variousfeatures, components and interrelationships therebetween of aspects ofan embodiment of the present disclosure are depicted. However, thepresent disclosure is not limited to the particular embodimentspresented and the components, features and interrelationshipstherebetween as are illustrated in the drawings and described herein.

DETAILED DESCRIPTION

The objectives and advantages of the claimed subject matter will becomeapparent from the following detailed description of the preferredembodiments thereof in connection with the accompanying drawings, inwhich like reference numerals denote like elements.

A system diagram of a fuel cell system 100 configured for internalreforming of a hydrocarbon fuel having a bypass in accordance with someembodiments of the present disclosure is illustrated in FIG. 1. Thesystem 100 comprises a fuel cell stack 102, a source of hydrocarbon fuel116, a reformer unit 118, and an oxidant source 150. The fuel cell stack102 comprises an anode portion 104 in fluid communication with an anodeinlet 106 and an anode exhaust 108, and a cathode portion 110 in fluidcommunication with a cathode inlet 112 and a cathode exhaust 114. Thefuel cell stack 102 may be of any fuel cell design and is preferably aSOFC.

The source of hydrocarbon fuel 116 may provide any type of hydrocarbonfuel, such as, e.g., methane, to the fuel cell system 100. The source ofoxidant 150 may provide air or other oxidant to the fuel cell system100.

The reformer unit 118 converts hydrocarbon fuel from the source ofhydrocarbon fuel 116 into a reformate and comprises one or morecold-side channels 120, a fuel supply conduit 122, a reformate exhaustconduit 124, one or more hot-side channels 126, a cathode exhaustconduit 128, a cathode inlet conduit 130, one or more bypass channels132, and a flow controller 134. In a preferred embodiment the reformerunit 118 is a steam reformer.

The cold-side channels 120 provide reforming passages that reform thefuel supplied from the source of hydrocarbon fuel 116 into a reformate.The cold-side channels 120 may be referred to as a reforming section.The reforming passages may contain a catalyst comprising at least oneGroup VIII metal, and preferably one Group VIII noble metal, such as,e.g., platinum, palladium, rhodium, iridium or a combination thereof. Acatalyst comprising rhodium and platinum are preferred. The catalyst maycontain active metals in any suitable amount that achieves the desiredamount of hydrocarbon conversion. For example, the active catalystmetals may comprise 0.1 to 40 wt % of the catalyst. In some embodiments,the active catalyst metals may comprise 0.5 to 25 wt % of the catalyst.In some embodiments, the active catalyst metals may comprise 0.5 to 15wt % of the catalyst.

In some embodiments, the catalyst may contain one or more promoterelements to improve the catalyst activity, durability, suppress carbonformation, or any combination of these or other improvements. Thepromoter elements may include, but are not limited to, elements fromGroups IIa-VIIa, Groups Ib-Vb, lanthanide and actinide series elements,or any combination thereof. Promoters such as magnesia, ceria, and bariamay suppress carbon formation. The promoter elements may be present inany amount ranging from 0.01 to 10 wt % of the catalyst. In someembodiments, the promoter elements may be present in amount ranging from0.01 to 5 wt % of the catalyst. The embodiments of the presentdisclosure are not so limited and may contain any amount of activemetal, promoter elements, or both in ranges outside of those expresslylisted.

The catalyst may be supported on a carrier comprising a refractory oxidesuch as, e.g., silica, alumina, titania, zirconia, tungsten oxides, andmixtures thereof, although the disclosure is not limited to refractoryoxides. In some embodiments, the carrier may comprise a mixed refractoryoxide compound comprising at least two cations. The catalyst active andpromoter elements may be deposited on the carrier by any of a number oftechniques. The catalyst may be deposited by impregnation onto thecarrier, e.g., by contacting the carrier materials with a solution ofthe catalyst followed by drying and calcining the structure. Thecatalyst may be coated onto the plates of a heat exchanger or on insertsplaced into the cold-side channels 120. Catalyst pellets of a suitablesize and shape may also be placed in the cold-side channel 120. However,the embodiments of the present disclosure are not so limited, and anymeans of incorporating the catalyst into the cold-side channels 120 maybe used, such as, e.g., using a porous support structure.

The cold-side channels 120 are in fluid communication with the source ofhydrocarbon fuel 116 via a fuel supply conduit 122 that functions totransport the hydrocarbon fuel from the source of the hydrocarbon fuel116 to the cold-side channels 120 of the reformer unit 118.

In accordance with some embodiments, the fuel cell system 100 mayfurther comprise a higher hydrocarbon reduction unit 148 which is influid communication with both the source of hydrocarbon fuel 116 and thefuel supply conduit 122. The higher hydrocarbon reduction unit 148 maybe used upstream of the reformer unit 118 to reduce the level of higherhydrocarbons fed to the reformer unit 118 cold-side channels 120 and thebypass channel 132. By reducing the level of higher hydrocarbons fed tothe reformer unit 118, the higher hydrocarbon reduction unit 148inhibits carbon formation within the fuel cell system 100.

As the hydrocarbon fuel passes through the reforming passages of thecold-side channels 120 it is at least partially reformed in a reformateor syngas (such as, e.g., hydrogen, or hydrogen and carbon monoxide).This reformate flows into the reformate exhaust conduit 124, which mayalso be referred to as an outlet plenum, that is in fluid communicationwith both the cold-side channels 120 and the anode inlet 106. Prior toreaching the anode inlet 106, the reformate in the reformate exhaustconduit 124 may reach a junction at which the reformate may be combinedand mixed with the flow of an unreformed hydrocarbon fuel flowingthrough the bypass channel 132. The unreformed hydrocarbon fuel flowingthrough the bypass channel 132 may flow through a heat exchanger 142,which may be referred to a second heat exchanging section. Heatexchanger 142 transfers heat from the cathode exhaust into theunreformed fuel. In some embodiments, the heat exchanger 142 may belocated upstream from the hot-side channels 126 rather than downstreamas depicted in FIG. 1. In some embodiments, the hot fluid flowingthrough heat exchanger 142 may be some fluid other than the cathodeexhaust, such as, e.g., the anode exhaust, gasses from a anode-exhaustrecycling combustor (such as combustor 146), or other source.

Reformer Unit 118 also comprises one or more hot-side channels 126,which may referred to as a heat exchange section. The hot-side channels126 provide a passage for a cathode exhaust gas to flow through thereforming unit 118. These channels 126 may be arranged in a sufficientlyclose proximity and orientation to the cold-side channels 120 in orderto effect the transfer of heat between fluids flowing in the hot-sidechannels 126 and the cold-side channels 120. The fluid flowing in thesechannels maybe oriented for parallel flow, counter flow, cross flow, orany other heat exchanger configuration. Regardless of the proximity ofthe heat exchange section to the reforming section, both components arearranged to be in thermal communication with one another.

The hot-side channels 126 of reformer unit 118 are in fluidcommunication with the cathode exhaust 114 via the cathode exhaustconduit 128. Additionally, the hot-side channels 126 may be in fluidcommunication with the cathode inlet 112 via the cathode inlet conduit130. In accordance with some embodiments, the cathode exhaust in thecathode inlet conduit 130 is supplied to the suction side of a cathodeejector 140. The oxidant source 150 may provide the motive energy whichoperates the cathode ejector 140. The cathode exhaust and oxidant mayflow through the cold-side channels of a heat exchanger 144 prior tobeing supplied to the cathode inlet 112. The hot-side channels of heatexchanger 144 may provide passage ways for a combustor 146 exhaust gasflow or other hot fluid which transfers heat into the combined cathodeexhaust-oxidant flow supplied to the cathode inlet 112.

The reformer unit 118 comprises one or more bypass channels 132, whichmay be referred to as a bypass section for providing a bypassing flowpath, that provide a non-reforming passage for hydrocarbon fuel to flowthrough the reformer unit 118. The bypass channel 132 is in fluidcommunication with the fuel supply conduit 122 and the reformate exhaustconduit 124. The unreformed hydrocarbon fuel from the bypass channel 132may be combined and mixed with the reformed fuel flowing through thereformate exhaust conduit 124. The bypass channel 132 may be a linecomprising a ceramic coating in order to inhibit metal-catalyzed carbonformation.

In accordance with some embodiments of the present disclosure,perspective views of a reformer having a bypass are illustrated in FIG.2A and FIG. 2B. A portion of the reformer unit 118 is illustrated ashaving a bypass channel 132. The bypass channel 132 may be a line (suchas, e.g., piping, hose, or similar component) connected proximate to andin fluid communication with the fuel supply conduit 122. As shown inFIG. 2B, the bypass channel 132 line may pass through the cathode inletconduit 130 prior to merging with the reformate exhaust conduit 124. Thecathode inlet conduit 130 may also be considered an exhaust duct throughwhich the cathode exhaust is removed from the reforming unit 118. Insome embodiments, the passage of the bypass channel 132 line through thecathode inlet conduit 130 will effect a heat transfer between the twofluids flowing in their respective sections. This arrangement mayprovide the function of heat exchanger 142, although the embodiments ofthe present disclosure are not so limited. The amount heat transferredbetween the cathode exhaust in the cathode inlet conduit 130 and theunreformed fuel in the bypass channel 132 may be effected by varying thelength of the bypass channel 132 line in the cathode inlet conduit 130.

In some embodiments, the one or more bypass channel 132 may beintegrated with the structure of the cold-side channels 120 and thehot-side channels 126 such that the channels 132 are in sufficientproximity to the hot-side channel 126 effect a heat transfer. In someembodiments, the one or more bypass channels 132 may be the equivalentof an un-catalyzed cold-side channels 120.

The reformer unit 118 may further comprise a flow controller 134, whichmay be referred to as a variable orifice flow controller, in the bypasschannel 132. The flow controller 134 may be an interchangeable floworifice. The flow controller restricts the flow of the unreformedhydrocarbon fuel by reducing the effective area of the bypass channel132. Controlling the flow rate of the unreformed hydrocarbon fuelflowing in the bypass channel 132 allows the precise control of theratio of reformate to unreformed fuel mixture supplied to the anode 104.

In accordance with some embodiments of the present disclosure, the fuelcell system 100 may further comprise one or more anode exhaust recyclelines. For example, a portion of the anode exhaust may be drawn into ananode ejector 138. The motive force for the anode ejector 138 may be thesource of hydrocarbon fuel 116, which may be pressurized by anyconventional means. The recycled anode exhaust may then be combined withthe source of hydrocarbon fuel 116 supplied to the reformer unit 118.

Another portion of the anode exhaust may be drawn into an auxiliaryejector 136. The auxiliary ejector 136 may be supplied by the oxidantsource 150. The combined oxidant—anode exhaust mixture may then flow toa combustor 146 that supplies a combustion product to the hot-sidechannels of heat exchanger 144. This combustion product may then bevented to the environment at 152. Other systems may be supplied withthese combustion products or other portions of the anode exhaust, e.g.,to power a turbine which may pressure various flows in the fuel cell.

In accordance with some embodiments of present disclosure, a variableorifice flow controller 300 is provided, which may be flow controller134 as described above. One embodiment of the flow controller 300 isillustrated in FIG. 3 to FIG. 5. FIG. 3 illustrates two perspectiveviews of a disassembled flow controller 300. The flow controller 300comprises an upstream connector 302, a downstream connector 310, and aninterconnector 316.

The upstream connector 302 may have a cylindrical tubular portion whichdefines a conduit 304 that is in fluid communication with a bypass flowpath designed to receive a fluid flowing through the bypass flow path.Other geometric configurations may be suitable for the conduit 304. Theupstream connector 302 may further comprise frusto-conical portion 306which defines a plurality of conduits 308. The plurality of conduits arein fluid communication with conduit 304.

The downstream connector 310 may define a frusto-conical cavity 312configure to receive the frusto-conical portion 306 of the upstreamconnector 302. The downstream connector 310 may further define aplurality of conduits 314 in fluid communication with the cavity 312.Additionally, the conduits 314 are in fluid communication with thereformate exhaust conduit and the anode inlet.

The plurality of conduits 308 and 314 may each be opposing, arcuateconduits, although other geometric designs may be used, and each conduit308 may form an opposing pair with a conduit 314.

The interconnector 316 may be a connection fitting designed to provide afluid-tight connection after the frusto-conical portion 306 is receivedwithin the frusto-conical cavity 312. The interconnector 316 maycomprise a plurality of internal threads (not shown) which engage aplurality of threads (not shown) on the downstream connector 310. Bytightening the interconnector 316 onto the downstream connector, thefluid-tight connection may be achieved. The fluid-tight connection maybe gastight, wherein the gas refers to the gas flowing through flowcontroller 300 or the gas surrounding the flow controller 300, such as,e.g., the atmosphere, or may refer to liquids. The interconnector 316may be a hose nut.

The amount of fluid communication between the plurality of conduits 308and 314, which may be considered the same as the flow rate through thebypass line, may be selected by the radial alignment between theupstream and downstream connectors 302 and 310, respectively. As shownin FIG. 4, the conduits 308 and 314 may be aligned to provide themaximum flow rate achievable for a give flow controller 300 design, orthe conduits 308 and 314 may be intentionally misaligned in order toreduce the effective flow area of the flow controller 300, therebyreducing the overall flow rate of the fluid in the bypass conduit.

The flow controller 300 may further comprise an alignment tab 318affixed to the upstream connector 302 and a plurality of alignmentnotches 320 on the downstream connector 310. The alignment tab 318 andnotches 320 function together to prevent the rotation of the upstreamconnector 302 around its long axis relative to the downstream connector310, thereby maintaining the desired alignment and, therefore, flowrate. In some embodiments the alignment of the conduits 308 and 314 ismaintained by compression fit rather than by use of the alignment tab318 and notches 320.

A perspective view of the assembled flow controller 300 is shown in FIG.5.

The flow controller 300 illustrated in FIGS. 3-5 is designed forapplications in which other designs would fail due to the hightemperature, high pressure, or both high temperature and pressure ofthose applications. These high temperatures may be caused by therecycled anode exhaust which may be supplied to the fuel cell systemreforming unit. Additional heat may be provided by a cathode exhaust gas(or other high temperature gas) heat exchanger which may be locatedupstream of the flow controller 300. For example, flow controller 300may be able to maintain a fluid-tight connection at temperatures of atleast 650 degrees Celsius, 700 degrees Celsius, 800 degrees Celsius, 850degrees Celsius, 900 degrees Celsius, or 950 degrees Celsius.

A flow controller 600 in accordance with some embodiments of the presentdisclosure is illustrated in FIG. 6 and FIG. 7. FIG. 6 illustrates theexploded, unassembled perspective view of the controller 600. Anassembled, perspective view of controller 600 may be seen in FIG. 7.This flow controller may function in a manner similar to the controller300 as described, and may contain components performing like functions.In the embodiment illustrated in FIG. 6 and FIG. 7, the downstreamconnector (not shown) may, or may not, define a plurality of conduits.The flow controller 600 may comprise a disc 622 that defines a pluralityof conduits 624. In accordance with some embodiments, the alignment ofthe plurality of conduits 308 and 624 will determine the amount of fluidcommunication in bypass line. An alignment tab 618 may be affixed to thedisc 622 and may be aligned with one of a plurality of notches 620 onthe upstream connector 302. When the upstream and downstream connectorsare in a fluid-tight connection, the alignment tab 618 and open of theplurality of notches 620 operate to prevent rotation of the disc 622relative to the upstream connector, and, therefore, maintain the amountof fluid communication between the plurality of conduits 308 and 624.The flow controller 600 may further comprise a retaining element 626,such as, e.g., a screw, which retains the disc 622 adjacent to a face628 of the frusto-conical portion 306 of the upstream connector 302.

The flow controller 600 illustrated in FIGS. 6-7 is designed forapplications in which other designs would fail due to the hightemperature, high pressure, or both high temperature and pressure ofthose applications. These high temperatures may be caused by therecycled anode exhaust which may be supplied to the fuel cell systemreforming unit. Additional heat may be provided by a cathode exhaust gas(or other high temperature gas) heat exchanger which may be locatedupstream of the flow controller 300. For example, flow controller 600may be able to maintain a fluid-tight connection at temperatures of atleast 650 degrees Celsius, 700 degrees Celsius, 800 degrees Celsius, 850degrees Celsius, 900 degrees Celsius, or 950 degrees Celsius.

In accordance with some embodiments of the present disclosure, areformer unit 800 having a bypass plenum is illustrated in FIGS. 8-12.FIG. 8 illustrates two perspective view of the reformer unit 800. FIG. 9is a close-up of the reforming section inlet 808. FIG. 10 is a close-upview of the bypass plenum 802. FIG. 11 illustrate a flow restrictor.FIG. 12 illustrates two perspective views, one being a cross section ofthe other, of the reforming section outlet plenum 812 and the bypassplenum 802 outlet 810.

The reformer unit 800 may comprise a reforming section 804 and a heatexchanging section 816 which may be the cold-side channels and hot-sidechannels, respectively, as described above. The reformer unit 800 mayfurther comprise a bypass plenum 802 having an inlet 806, an outlet 810,and a flow restrictor 814. The inlet 806 may be in fluid communicationwith the reforming section inlet 808 and be configured to receive aportion of the unreformed hydrocarbon fuel-anode exhaust mixture flowingthereto. The outlet 810 is in fluid communication with the reformingsection outlet plenum 812 such that the bypass plenum 802 and reformingsection 804 flow paths may converge and mix prior to being supplied tothe anode. The flow restrictor 814 may be disposed in a flow pathbetween the outlet 810 of the bypass plenum 802 and the outlet plenum812 of the reforming section 804.

The heat exchanging section 816 of the reformer unit 800 may beconfigured to be in thermal communication with the bypass plenum 802.For example, the bypass plenum may share or have one or more walls incontact with the heat exchange section 816. This will effect a heatexchange between the cathode exhaust, or other hot fluid, flowingthrough the heat exchanging section 816 to provide thermal energy to thebypass flow prior to that flow being merged with the reformed fuel fromthe reforming section 804. In some embodiments, the flow of cathodeexhaust or other hot fluid in the heat exchange section 816 may beconfigured to exchange heat with the fluid in the bypass plenum 802prior to exchanging heat with fluid in the reforming section 804. Inother embodiments, the flow of cathode exhaust or other hot fluid in theheat exchange section 816 may be configured to exchange heat with thefluid in the reforming section 804 prior to exchanging heat with fluidin the bypass plenum 802. The first occurring heat transfer may also bereferred to as an upstream thermal communication. Whether the heatexchange between the fluid in the heat exchange section 816 occurs firstwith the bypass plenum 802 or the reforming section 804 may becontrolled by, e.g., selecting the direction of flow of the cathodeexhaust or other hot fluid.

As shown in FIG. 12, the outlet 810 of the bypass plenum 802 may definean orifice 818 providing fluid communication between the bypass plenum802 and the outlet plenum 812 of the reforming section 804. The flowrestrictor 814 may comprise an elongated member 822 (also referred to asa flow restricting member or an elongated flow restricting member) whichextends into the orifice to reduce its cross-sectional area and restrictthe fluid flowing there through.

Alternate views of the flow restrictor 814 are provided in FIG. 11. Theflow restrictor 814 may comprise a connector 820 and the flowrestricting member 822. The connector 820 may be mounted to the reformerunit 800 on a wall of the bypass plenum 802.

The flow restricting member 822 may be elongated and removably carriedby the connector 820. The member 822 extends through the orifice 818,thereby reducing its effective cross-sectional area. The flow rate ofthe fluid flowing between the bypass plenum 802 and the outlet plenum812 of the reforming section 804 is selected by sizing the flowrestricting member 822 relative to the orifice 818. The flow restrictingmember 822 may be cylindrical. In some embodiments the flow restrictingmember 822 may have an oval or rectangular cross-section or may beconical or other suitable shape. The elongated member 822 may have athreaded portion (not shown) for engaging the connector 820.

In some embodiments, the flow restricting member 822 may have a taperedcross-section. The flow rate between the bypass plenum 802 and theoutlet plenum, 812 may be determined by the sizing of the member 822 andthe orifice 818 and by the axial alignment between the two parts. Thisaxial alignment may be set by rotating a threadably engaged member 822within a threaded (not shown) connector 820.

The connector 820 may have a first portion defining a cylindrical cavityhaving a threaded portion for engaging the elongated member 822, and mayfurther have a second portion which may define a frusto-cylindricalcavity in communication with the cylindrical cavity. This cavity mayaccept a fitting 824 having a frusto-cylindrical portion defining anaxial slot. The elongated member 822 may further comprise a portionwhich extends into this axial slot, thereby preventing rotation of theelongated member 822 while the fitting is installed. In someembodiments, rotation of the elongated member may be prevented when thenut 826 operably engages connector 820 to provide a fluid-tight seal.

The flow restrictor 814 may further comprise an internally threadedsealing nut 826 which may engage external threading on the connector820, thereby providing a fluid-tight seal between the fitting 824 andthe connector 820 when nut 826 is tightened on connector 820.Additionally, fitting 824 may be engaged by the nut 826 to preventleakage of system fluid around member 822.

The flow restrictor 814 illustrated in FIGS. 8 and 10-12 is designed forapplications in which other designs would fail due to the hightemperature and pressure of those applications. These high temperaturesmay be caused by the recycled anode exhaust which may be supplied to thefuel cell system reforming unit. Additional heat may be provided by acathode exhaust gas (or other high temperature gas) heat exchangingsection 816. For example, flow restrictor 814 may be able to maintain afluid-tight connection at temperatures of at least 650 degrees Celsius,700 degrees Celsius, 800 degrees Celsius, 850 degrees Celsius, 900degrees Celsius, or 950 degrees Celsius.

While preferred embodiments of the present subject matter have beendescribed, it is to be understood that the embodiments described areillustrative only and that the scope of the subject matter is to bedefined solely by the appended claims when accorded a full range ofequivalence, and the many variations and modifications naturallyoccurring to those of skill in the art from a perusal hereof.

We claim:
 1. A reformer unit for a fuel cell system comprising: areforming section for reforming a hydrocarbon-containing fuel, saidreforming section having an inlet adapted for fluid communication with asource of hydrocarbon-containing fuel, and an outlet plenum adapted forfluid communication with an anode inlet of a fuel cell stack; a heatexchanging section for heating a fluid flowing in the reforming section,said heat exchanging section having an inlet adapted for fluidcommunication with an exhaust of a cathode of a fuel cell stack, and anoutlet adapted for fluid communication with an inlet of a cathode of thefuel cell stack, said heat exchanging section being in thermalcommunication with said reforming section to effect heat transferbetween a fluid flowing through said heat exchanger section and a fluidflowing through said reforming section; and a bypass plenum forproviding a bypassing flowpath for a hydrocarbon-containing fuel aroundsaid reforming section, said bypass plenum having an inlet in fluidcommunication with said reforming section inlet, an outlet in fluidcommunication with said reforming section outlet plenum, and a flowrestrictor in a flowpath between the outlet of said bypass plenum andthe outlet plenum of said reforming section, wherein the outlet of saidbypass plenum defines an orifice providing fluid communication betweensaid bypass plenum and the outlet plenum of said reforming section, andwherein said flow restrictor comprises: a connector mounted to a wall ofsaid bypass plenum; and an elongated flow restricting member carried bysaid connector, said elongated flow restricting member having a taperedcross-section and extending through the orifice defined by said bypassplenum to thereby reduce the cross-sectional area of the orifice throughwhich a fluid may flow, whereby the flow rate of fluid flowing betweensaid bypass plenum and the outlet plenum of said reforming section isselectable by selecting the axial alignment between said flowrestricting member relative to the orifice to thereby select thecross-sectional area of the orifice through which a fluid may flow. 2.The reformer unit of claim 1, wherein said heat exchanging section is inthermal communication with said bypass plenum to effect heat transferbetween a fluid flowing through said heat exchanger section and a fluidflowing through said bypass plenum.
 3. The reformer unit of claim 2,wherein said thermal communication is provided through a wall shared bysaid bypass plenum and said heat exchanging section.
 4. The reformerunit of claim 2, wherein said thermal communication between said heatexchanging section and said bypass plenum is upstream of the thermalcommunication between said heat exchanging section and said reformingsection.
 5. The reformer unit of claim 2, wherein said thermalcommunication between said heat exchanging section and said reformingsection is upstream of the thermal communication between said heatexchanging section and said bypass plenum.
 6. The reformer unit of claim1, wherein the outlet of said bypass plenum defines an orifice providingfluid communication between said bypass plenum and the outlet plenum ofsaid reforming section, and wherein said flow restrictor comprises: aconnector mounted to a wall of said bypass plenum; and an elongated flowrestricting member removably carried by said connector, said elongatedflow restricting member extending through the orifice defined by saidbypass plenum to thereby reduce the cross-sectional area of the orificethrough which a fluid may flow, whereby the flow rate of fluid flowingbetween said bypass plenum and the outlet plenum of said reformingsection is selectable by selecting the size of said flow restrictingmember relative to the orifice.
 7. The reformer unit of claim 6, whereinsaid orifice is circular in cross section and said elongated flowrestricting member is cylindrical.
 8. The reforming unit of claim 6,wherein said flow restrictor forms a fluid-tight connection for a fluidhaving a temperature of at least 650° C.
 9. The reformer unit of claim1, wherein said elongated flow restrictor member comprises a conicalportion extending through said orifice and a threaded portion threadablyengaged with said connector, wherein the axial alignment of said conicalportion is selectable by rotating said flow restrictor member relativeto said connector.
 10. A reformer unit for a fuel cell systemcomprising: a reforming section for reforming a hydrocarbon-containingfuel, said reforming section having an inlet adapted for fluidcommunication with a source of hydrocarbon-containing fuel, and anoutlet plenum adapted for fluid communication with an anode inlet of afuel cell stack; a heat exchanging section for heating a fluid flowingin the reforming section, said heat exchanging section having an inletadapted for fluid communication with an exhaust of a cathode of a fuelcell stack, and an outlet adapted for fluid communication with an inletof a cathode of the fuel cell stack, said heat exchanging section beingin thermal communication with said reforming section to effect heattransfer between a fluid flowing through said heat exchanger section anda fluid flowing through said reforming section; and a bypass plenum forproviding a bypassing flowpath for a hydrocarbon-containing fuel aroundsaid reforming section, said bypass plenum having an inlet in fluidcommunication with said reforming section inlet, an outlet in fluidcommunication with said reforming section outlet plenum, and a flowrestrictor in a flowpath between the outlet of said bypass plenum andthe outlet plenum of said reforming section, wherein said flowrestrictor comprises: a connector mounted to a wall of said bypassplenum comprising a first portion defining a cylindrical cavity having athreaded portion and a second portion defining a frusto-cylindricalcavity in communication with said cylindrical cavity; a fittingcomprising a frusto-conical end portion positioned within saidfrusto-conical cavity, said frusto-conical portion defining an axialslot; an elongated flow restricting member comprising a cylindricalthreaded portion positioned within and threadably engaged with saidcylindrical cavity, a portion extending from one end of said cylindricalportion into said slot, and a tapered portion extending from the otherend of said cylindrical portion through said orifice, wherein the axialalignment of said tapered portion and said orifice is selectable byrotation of said flow restricting member relative to said connector; andan internally threaded sealing nut engaging an external threaded portionof said connector for providing an gastight seal between said fittingand said connector.
 11. The reforming unit of claim 10, wherein saidflow restrictor forms a fluid-tight connection for a fluid having atemperature of at least 650° C.
 12. The reforming unit of claim 10,wherein said slot operably engages said portion of the elongated flowrestricting member to prevent rotation of said elongated flowrestricting member when said nut engages said external threaded portionof said connector to provide a gastight seal.
 13. A reformer unit for afuel cell system comprising: a reforming section for reforming ahydrocarbon-containing fuel, said reforming section having an inlet andan outlet plenum; a bypass plenum for providing a bypassing flowpath fora hydrocarbon-containing fuel around said reforming section, said bypassplenum having: an inlet in fluid communication with said reformingsection inlet; an outlet in fluid communication with said reformingsection outlet plenum; and a flow restrictor in a flowpath between theoutlet of said bypass plenum and the outlet plenum of said reformingsection; said flow restrictor comprising: a connector mounted to a wallof a first plenum, said connector comprising a first portion defining acylindrical cavity having a threaded portion and a second portiondefining a frusto-cylindrical cavity in communication with saidcylindrical cavity; a fitting comprising a frusto-conical end portionpositioned within said frusto-conical cavity, said frusto-conicalportion defining an axial slot; an elongated flow restricting membercomprising a cylindrical threaded portion positioned within andthreadably engaged with said cylindrical cavity, a portion extendingfrom one end of said cylindrical portion into said slot, and a taperedportion extending from the other end of said cylindrical portion throughthe orifice, wherein the axial alignment of said tapered portion and theorifice is selectable by rotation of said flow restricting memberrelative to said connector; and an internally threaded sealing nutengaging an external threaded portion of said connector for providing angastight seal between said fitting and said connector; and a heatexchanging section being in thermal communication with said reformingsection to effect heat transfer between a fluid flowing through saidheat exchanger section and a fluid flowing through said reformingsection, and in further thermal communication with said bypass plenum toeffect heat transfer between a fluid flowing through said heat exchangersection and a fluid flowing through said bypass plenum.
 14. The reformerunit of claim 13, wherein said slot operably engages said portion of theelongated flow restricting member to prevent rotation of said elongatedflow restricting member when said nut engages said external threadedportion of said connector to provide a gastight seal.
 15. The reformerunit of claim 13, wherein said flow restrictor forms a gastightconnection for a gaseous fluid having a temperature of at least 650° C.